Injuries due to exposure - Altitude sickness

Traveling to high altitudes exposes travelers to increasingly rarefied air and progressively decreasing amounts of oxygen, resulting in declining levels of oxygen in the blood and thus impaired physical and mental performance. The response to high altitudes varies from individual to individual, but most people can operate normally at heights up to 8,000 feet (2,438 meters) above sea level. At altitudes greater than that, the oxygen deficit can begin to cause a condition known as acute mountain sickness (AMS). At elevations over 10,000 feet (3,048 meters), 75 percent of people will experience at least mild AMS symptoms.

Signs and symptoms: (Symptoms of a disease are subjective indications that can be detected by a patient, such as pain or fatigue, while signs are objective indications that can be detected by a doctor, such as temperature or pulse.) The onset of AMS symptoms varies according to the altitude, your rate of ascent, and your individual susceptibility to the disease. A slow ascent is more likely to allow your body to acclimate, by establishing a more rapid spontaneous breathing rate to make up for the decreased oxygen in the atmosphere. Symptoms usually start from 12 to 24 hours after your arrival at altitude and begin to decrease in severity by about your third day at a given elevation.

Mild AMS causes travelers to feel generally unwell. They may also suffer a loss of appetite, headache, lightheadedness, fatigue, breathlessness, rapid heartbeat, nausea, and/or difficulty sleeping. Symptoms tend to be worse at night. Mild AMS does not interfere with normal activities, and symptoms generally subside within two to four days, as the body acclimates.

Severe AMS manifests itself in the form of serious conditions known as high-altitude pulmonary edema (HAPE) or high-altitude cerebral edema (HACE) — the accumulation of excess fluid in the lungs or brain. The symptoms of severe AMS include a gray or pale complexion, a blue tinge to the skin (a condition known as cyanosis), chest tightness or congestion, cough, coughing up blood, difficulty walking, shortness of breath when at rest, withdrawal from social interaction, confusion, and/or decreased consciousness. Severe AMS can be fatal if it's not treated or the victim is not returned to a lower altitude.

EFFECTS OF INCREASING ALTITUDESea level:* Atmospheric pressure is 765 mmHg (millimeters of mercury, the unit of measure for pressure in gases and liquids).* Partial pressure of atmospheric oxygen is 160 mmHg.* Arterial oxygen pressure (PaO2) is 80 to 100 mmHg.* Arterial carbon dioxide pressure (PaCO2) is 38 to 42 mmHg.High altitude — 8,000 to 12,000 feet (2,438 to 3,658 meters):* Commercial aircraft cabin pressure is typically equivalent to the pressure at about 8,000 feet (2,438 meters).* Altitude sickness is common above 8,000 feet (2,438 meters).* The availability of oxygen drops to 90 to 65 percent of the amount at sea level.* Arterial PaO2 is significantly diminished.* Exercise performance decreases and ventilation (the exchange of air between the lungs and the atmosphere) increases due to lower arterial PaCO2.Very high altitude — 12,000 to 18,000 feet (3,658 to 5,486 meters):* Atmospheric pressure is 483 mmHg or less.* The availability of oxygen drops to 65 to 50 percent of the amount at sea level.* Arterial PaO2 falls below 60 mmHg.* Extreme hypoxemia (an abnormally low concentration of oxygen in the blood) may occur during exercise and sleep.* Severe altitude sickness occurs most commonly in this range.Extreme altitude — above 18,000 feet (5,486 meters):* The availability of atmospheric oxygen drops below 50 percent of the amount at sea level.* Marked hypoxemia, very low PaCO2, and alkalosis (excessive alkalinity of the body fluids) are likely to occur.* All physiological functions progressively deteriorate.* No permanent human habitation exists above 20,000 feet (6,096 meters).Treatment: Responding promptly to signs or symptoms of AMS is essential. It is advisable to call the nearest emergency medical service (EMS) immediately if you or someone traveling with you experience any of the following symptoms:* Severe breathing problems* Altered level of alertness* Coughing up bloodIf you cannot count on EMS aid, get the affected individual down to a lower altitude as quickly and as safely as possible and administer oxygen if it's available. Also, keep victims warm and, if they're conscious, be sure they stay well hydrated.

To avoid altitude sickness, it's important to ascend slowly enough to allow time for your body to acclimate. Some people also find it beneficial to take prophylactic medication to help with the acclimatization process and/or to prevent some ill effects. If you plan to travel to a high-altitude location, visit your doctor or a travel clinic before your trip to evaluate your risk of altitude sickness and to obtain prophylactic medication that may prevent or alleviate AMS.

Anybody can be affected by AMS. You are at higher risk if:* You live at or near sea level and travel to a high altitude.* You have had AMS before.* You have pre-existing medical conditions.* You ascend quickly to a high elevation.Do not travel to a high-altitude location if you have a heart, lung or blood disorder without consulting your doctor. You may need to travel with supplemental oxygen.

Following these strategies can help to prevent and/or moderate AMS:* Do not ascend quickly above 8,000 feet.* If you travel to high altitudes, choose a slow transportation method or walk.* If you get there by flying, do not overexert yourself or travel still higher for the first 24 hours.* If you travel above 10,000 feet (3,048 meters), increase your altitude by no more than 1,000 feet (305 meters) per day.* After every 3,000 feet (914 meters) of elevation gained, take a rest day.* After daily excursions, return to a lower altitude for the night, if possible.* Don't go higher if you experience any AMS symptoms; wait for the symptoms to decrease first.* If your symptoms increase, go down!* Stay properly hydrated. Drink at least three to four quarts of fluids per day, and be sure to quench your thirst. Make sure to urinate regularly.* Light activity during the day is better than sleeping, because respiration decreases during sleep, exacerbating AMS symptoms.* Avoid tobacco, alcohol and depressant drugs (such as barbiturates, tranquilizers, and sleeping pills), all of which worsen AMS symptoms.* Eat a high-carbohydrate diet while at altitude, but do not overeat.

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